In a device to monitor a radio wave radiated in the air, due to reception of the radio wave as multipath waves in which a direct wave and reflected waves (delayed waves) coming through various reflection paths are included, there are cases in which demodulation becomes difficult, a signal level of a received signal is dropped, or a signal cannot be analyzed.
A scheme referred to RAKE reception described in Non-Patent Literature 1 can be cited for solving the influence of the multipath waves. Regarding the multipath waves of a signal having a broad frequency band such as a spectrum diffusion signal, the RAKE reception can improve performance of demodulating the received signal by means of pass diversity. However, the effectiveness of the RAKE reception is limited to a signal having a broad frequency band such as the spectrum diffusion signal.
For example, as in Patent Literature 1, the sparse vector estimation method is proposed for use in angle measurement processing such as in a radar. The observation equipment of Patent Literature 1 estimates a relative distance to an object-to-be-observed using a distance measurer. An angle measurer adjusts an internal parameter in the estimation process in response to the relative distance to the object-to-be-observed estimated in the distance measurer, and estimates a direction to which the object-to-be-observed exists.